In recent years, various thermal insulation coating materials have been proposed for forming thermal insulation coating films on building roofs and roads as one of the increasingly demanding energy-saving measures (for example, see Patent Documents 1 and 2). Coloring of these thermal insulation coating materials may be performed by a technique according to the subtractive color mixing method using a pigment with high infrared-light reflectance, such as titanium dioxide.
Meanwhile, a pigment having infrared-light reflective capability may, in nature, reflect visible-light as well. The selection of pigments in coloring may also be very limited. For example, a coloring pigment with less infrared-light absorption needs to be selected. Further, a dark color system such as black in particular may reduce infrared-light reflectance because of its low content ratio of titanium dioxide in a pigment. Therefore, the above technologies currently can not be used for applications requiring sophisticated designs such as automobile bodies. To meet requirements for these uses, there have been demands for an infrared-reflective pigment having both high infrared-light reflectivity and high visible-light transparency.
For example, as pigments which can reflect infrared light, but allow visible light to transmit, proposed are those including transparent electrically-conductive inorganic particulates such as ITO (tin-doped indium oxide) and ATO (antimony-doped tin oxide) (For example, see Patent Document 3), those including nano-sized hexaboride particulates as a heat-ray insulation component (for example, see Patent Document 4), optical coherence pigments with multilayered films of oxides (for example, see Patent Document 5). Heat-ray insulation plates also have been proposed in which titanium dioxide, or inorganic particles such as mica coated with titanium dioxide, which have heat-ray reflective capability, are kneaded in a transparent resin (for example, see Patent Documents 6 and 7).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2002-20647
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2002-320912
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2001-262016
Patent Document 4: Japanese Unexamined Patent Application, Publication No. 2004-162020
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2004-4840
Patent Document 6: Japanese Unexamined Patent Application, Publication No. H05-78544
Patent Document 7: Japanese Unexamined Patent Application, Publication No. H02-173060